Jointing of composite fabrics

ABSTRACT

Compositive fabric comprising spaced apart linear yarns extending in the longitudinal plane of the fabric, wherein at least some of said yarns are turned back and extend at least partially back through the fabric in said spaced apart relationship, wherein the yarns are interconnected and encapsulated by a homogenous matrix material leaving free loops extending from at least one end of the matrix material which are formed by the apexes of the turned back yarns.

The present invention relates to composite fabrics and the jointing ofcomposite fabric ends, and has particular, though not exclusive,reference to the jointing together of the opposed ends of a papermakersdryer fabrics or like industrial fabric so as to bring the same into anendless band.

A non-woven membrane which is suitable for use in paper machine clothingand its method of manufacture is described in UK patents GB 2,202,873(Lefkowitz) and GB 2,235,705 (Lefkowitz). This prior non-woven membranehas a knuckle free planar surface comprising a lattice structure ofinterconnecting machine and cross-machine direction polymeric structuralmembers residing in a single plane which define a matrix of spacedapertures there between. A proportion of the machine direction landscontain an encapsulated machine direction yarn.

One process for the production of such a composite membrane is describedin U.S. Pat. No. 4,740,409. In this method, load bearing yarns are fedfrom a creel to lie within the zone of an extruder die. The extruderfeeds a molten matrix, accompanied by the yarns, onto a pinned surfaceof a casting drum. This creates a perforated tape which is allowed tocool to the point where it can be removed from the casting drum.

To yield a fabric of useful size, the tape is then directed around atail roller and returned to a position alongside the polymer melt,having first been relocated back on the pinned drum. The edge of thetape is softened, or more specifically, re-melted so that it can combinewith the adjacent extrudate. An endless porous sheet results, consistingof continuously joined porous tapes whose boundaries are barelydiscernable. Given that the attendant machinery is large enough, thereis no limit to the size of fabric which can be produced.

Alternatively, the membrane can be formed by feeding a respective one ofan array of bi-component yarns, the core of which has a higher meltingpoint than that of the sheath, into every second or third peripheralgroove of a pinned roller which is arranged in nip forming relationshipwith a press roll. The material of the sheath is first melted and thenthe yarns move into and through the roller nip whereupon the meltedsheath material is forced into lateral grooves and the vacantlongitudinal grooves in the roller. Upon cooling, the melted materialsets to provide the machine and cross-machine structural members to thefinished membrane.

A further method to produce a composite membrane suitable for use as adryer fabric is described in WO 91/02642 (Huyck Corporation). This priormethod uses two pre-cast rolls of thermoplastic film with machinedirection reinforcing yarns being introduced as the middle of thesandwich. With films of polymers with high melt temperatures,pre-heating of these films may be required before they advance towardsthe forming zone, where they are merged into a single entity by means ofpressure and heat.

For many years considerable attention has been directed to the provisionof seam forming elements at the respective ends of woven dryer fabrics,whereby said ends might be securely and uniformly joined in such amanner that the permeability in the seam region is not materiallydifferent from that of the body of the fabric.

Originally dryer fabric seaming was effected either by sewing, orotherwise securing, a substrate carrying laterally extending loops toeach of respective fabric ends or by folding back and sewing the fabricedges to create a seam and inserting a spiral, the loops at therespective ends being interdigitated and a pintle wire introduced intothe tunnel formed by the interdigitated loops to hold the ends together.

Another well practised procedure is to “weave-back” free warp ends intothe body of the fabric and in so doing form loops from the individualwarp yarns at the ends of the fabric, which can then be interdigitatedand a pintle wire introduced as described above. Alternatively, apreformed spiral yarn can be inserted into the aforementioned said loopsand used to seam the fabric.

EP 0,399,674 discloses a method of seaming a composite dryer fabricwhich is an adaptation of the technique of weaving back the free warpyarns of a woven fabric. In this prior technique naked machine directionyarns extend from either end of the composite fabric, these free yarnends are folded back upon themselves and encapsulated on a mouldingplate, to provide free loops at either end of the fabric which can beinterdigitated and a pintle inserted therein to render the fabricendless.

However, the above described method is not ideal for joining compositefabric ends, in that the seam region is provided with a double layer ofmonofilament yarn, which can make the fabric stiff in the seam area andtherefore more difficult to install on a machine.

It is an object of the present invention to provide a composite fabric,a method of jointing a composite fabric, and a composite fabric seamwhich overcomes or alleviates the above described drawback.

In accordance with a first aspect of the present invention there isprovided a composite fabric comprising spaced apart linear yarnsextending in the longitudinal plane of the fabric, wherein at least someof said yarns are turned back and extend at least partially back throughthe fabric in said spaced apart relationship, wherein the yarns areinterconnected and encapsulated by a homogeneous matrix material leavingfree loops extending from at least one end of the matrix material whichare formed by the apexes of the turned back yarns. This structure hasthe advantage that it negates the disadvantages associated with foldingback the yarns on themselves to provide the loops, in that the doublethickness of the yarns in the region of the seam is not present, whichdouble thickness can render the fabric stiff making it difficult toinstall on a machine.

The turned back portion of the yarn within the matrix material may beconnected to a separate yarn running along the same line and at aposition remote from the fabric end.

The open part of the loop may extend in a substantially transverse planeto the longitudinal extent of the fabric. This enables easyinterdigitation of opposed fabric ends and insertion of a pintle wire tomake a longer and/or endless fabric. By controlling the sizes of fabriclengths added on, an endless fabric of the desired length can be readilyconstructed.

The matrix material may have apertures therein in lateral offsetdisposition relative to the yarns and extending throughout the fabric.

In accordance with a second aspect of the present invention there isprovided a method of manufacture of a jointed or seamed composite fabriccomprising the steps of making a first strip of fabric by providing anarray of spaced apart yarns extending in a first plane, turning back atleast some of the yarns in order that they extend at least partiallyback in said spaced apart relationship in said plane, and encapsulatingsaid yarns in a homogeneous matrix material to leave free loopsextending from one end of the matrix material formed by the apex of theturned back yarns.

Preferably, the step of encapsulation involves leaving free yarnsprotruding from the other end of the matrix material.

In one embodiment the method further includes the steps of providing asecond strip of fabric by providing a corresponding second array ofspaced apart yarns extending in a first plane and encapsulating saidyarns in said matrix material to leave free yarns protruding from atleast one end of the matrix material.

The method may further involve the step of joining opposed ends of thefirst and second fabric portions of the fabric to make a longer fabricby placing in contact a respective free yarn of one portion with arespective corresponding free yarn of the other portion andinterconnecting and encapsulating said contacting yarns in said matrixmaterial to form a homogeneous length of fabric. The step ofinterconnecting said contacting free yarns also includes the step ofjoining said free yarns before encapsulation in said matrix material. Inone embodiment respective joints of the yarns are not substantiallyaligned. This has the advantage of reducing areas of localised weakness.The method may include the step of joining the opposed loop bearing endsof two first sections of fabric by interdigitating the loops of theopposed ends and then interconnecting the two portions with a pintle.This has the advantage that a particular length of fabric can beconstructed from the interconnection of a plurality of first and/orsecond fabric portions and the fabric can be rendered endless byproviding two first, loop bearing portions at opposite ends of a fabriclength thus constructed and interconnecting with a pintle. This has theadditional advantage that main body sections can be made in advance, andwhen constructing the fabric appropriately sized jointing strips can beadded to make the fabric up to the desired size.

The method further includes the step of providing a plurality ofapertures in the matrix material in lateral offset disposition relativeto the yarns and extending throughout the material. The apertures may beformed during the encapsulation of the yarns by placing each of thearray of yarns and/or turned back yarns and/or joined yarns into arespective groove of a mould comprising upstanding pins serving to formsaid apertures in said material and then encapsulating the yarns, withinthe matrix material of the mould.

The invention will now be described further, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 through 5 are schematic views showing the steps in theconstruction of a composite fabric in accordance with one embodiment ofthe present invention.

A composite fabric is constructed in accordance with one of the methodsdisclosed in GB 2,202,873 or GB 2,235,705, as described earlier. Thefabric comprises a knuckle free non-woven membrane 2 as best illustratedin FIG. 1, having a planar surface comprising a lattice structure ofinterconnecting machine and cross-machine direction polymeric structuralmembers 4, 6 residing in a single plane which define a matrix of spacedapertures 8 therebetween. Each of the machine direction (md) lands 4contains an encapsulated md yarn 10. The membrane 2 forms the main bodyof the fabric.

However, in an adaptation to this prior method a length 10A of each yarn10 is left free at each end of the membrane, the length of the freeportion of the yarns 10A being in the range of 1 to 500 mm, typically 50mm.

A jointing strip 12, as best illustrated in FIG. 2, of a similarconstruction to main body 2 is also formed such that it has the samewidth, as measured in the intended cross-machine direction, and the samethickness as that of membrane 2. The jointing strip 12 however is likelyto be of a much shorter length, that is typically 5 to 500 cm, whenmeasured in the intended machine direction. Similar to the main body 2the jointing strip 12 has free yarns 10A extending from one end thereof,but has loops 14 formed from the yarns 10 extending from the oppositeedge thereof.

The jointing strip 12 is formed on a pinned mould plate 11 having aplurality of upstanding pins 13 having the same configuration as that ofthe pinned drum used to construct the main body of the fabric. In thisinstance, the yarns would initially be placed through alternativegrooves 15 of the mould plate (FIG. 3) and then looped back and passedthrough the respective adjacent empty groove 17 prior to beingencapsulated in the polymeric material to provide lattice membranestructure with embedded md yarns. This fixes the loops in place suchthat they protrude from one edge of the membrane structure,substantially in a transverse plane to the longitudinal extent thereofas illustrated in FIG. 2. It also leaves free yarns 10A extending from,the opposite edge of the membrane structure.

As best illustrated in FIG. 4, the jointing strip 12 is then joined tothe main body 2, by overlapping their respective protruding yarns 10Aand interlocking these yarns together. Each pair of joined yarns isplaced in a respective groove of a pinned mould plate, whose upstandingpins have the same effective configuration as that of the pinned roller.These yarns are then embedded in the molten matrix material usingwhichever method has been chosen. Upon cooling, the resultant machineand cross-machine direction lands formed are consistent with those themain body 2 and the jointing strip 12. This provides a like permeabilitycharacteristic to this region, when compared to that of the remainder ofthe fabric, and with the machine-direction yarns encapsulated within themd lands provides an invisible joint between the main body 2 and thejointing strip 12.

A similar jointing strip 12 is joined to the opposite end of the mainbody 2 in the same manner to form the completed composite fabric.

The composite fabric can be formed into an endless loop byinterdigitating the loops 14 at the opposing ends and interconnectingsuch with a pintle in a known manner. For this purpose the loops 14 atone end tilt to one side, whilst the loops of the opposite end have acomplementary tilt such that they evenly overlap when interdigitated.

Methods of joining the free yarns 10A of the main body 2 and jointingstrip 12, could include techniques such as ultrasonic welding chemicalbonding adhesive means, crimping and other mechanical means. Thejointing of the yarns may also be staggered with respect to the width ofthe fabric, to avoid a line of localised weakness. The individual jointshave been illustrated in FIG. 4 in such a staggered manner. Although thefree yarns have been described as being overlapped beforeinterconnection, they may alternatively be laser welded. In thisinstance, for example, near infrared (NIR) e.g. CO₂ laser could be used,aided by a thin layer of material which concentrates the laser energy atthe interface. Further it is possible to use diode lasers or ionic diodelasers.

Although the jointing strip has been described as being formed on apinned mould plate, it could alternatively be produced on the othermeans such as on a pinned roller.

Although a yarn has been described as being present in everymachine-direction land of the composite fabric, some such machinedirection lands may not contain yarn. Also, cross-machine directionyarns may additionally be provided in some or all of the cross-machinedirection lands. Alternatively, other cross-machine direction supportcould be included.

Although the method of production has been described with reference tothose described in GB 2,202,873 and GB 2,235,705, other methods ofproduction of the main composite fabric bodies could be used providedthat free yarns protrude from each edge of the main body. The matrixmaterial of the fabric may be formed from polymeric materials such aspolyesters, polyamides, polyimides polyolefines, PPS, PCTA, polyurethaneand rubber based materials. These would typically be processed by somesort of melt processing, as would in general be applied to thermoplasticsystems. In some cases it may be desirable to secondary cure thefinished product to give a thermoset, e.g. through the use ofelectromagnetic irradiation.

If the matrix material is being added into the mould plate or pinnedroller such could be provided in a particulate, or liquid form or indeeda sheet of such material which is then brought into liquid form byapplication of heat.

It should be understood that the foregoing description and drawings arenot intended to be limiting, but are only exemplary of the inventivefeatures which are defined in the claims.

1. Composite fabric comprising spaced apart linear yarns extending inthe longitudinal plane of the fabric, wherein at least some of saidyarns are turned back and extend at least partially back through thefabric in said spaced apart relationship, wherein the yarns areinterconnected and encapsulated by a homogeneous matrix material leavingfree loops extending from at least one end of the matrix material whichare formed by the apexes of the turned back yarns.
 2. Composite fabricaccording to claim 1, wherein the turned back portion of the yarn withinthe matrix material may be connected to a separate yarn running alongthe same line and at a position remote from the fabric end.
 3. Compositefabric according to claim 1 or 2, wherein the open part of the loopextend in a substantially transverse plane to the longitudinal extent ofthe fabric.
 4. Composite fabric according to one of the precedingclaims, wherein the matrix material have apertures therein in lateraloffset disposition relative to the yarns and extending throughout thefabric.
 5. Composite fabric according to one of the preceding claims,wherein joints of the yarns are not substantially aligned.
 6. Method ofmanufacture of a jointed or seamed composite fabric comprising the stepsof making a first strip of fabric by providing an array of spaced apartyarns extending in a first plane, turning back at least some of theyarns in order that they extend at least partially back in said spacedapart relationship in said plane, and encapsulating said yarns in ahomogeneous matrix material to leave free loops extending from one endof the matrix material formed by the apex of the turned back yarns. 7.Method according to claim 6, wherein the step of encapsulation involvesleaving free yarns protruding from the other end of the matrix material.8. Method according to claim 6 or 7, wherein the method further includesthe steps of providing a second strip of fabric by providing acorresponding second array of spaced apart yarns extending in a firstplane and encapsulating said yarns in said matrix material to leave freeyarns protruding from at least one end of the matrix material.
 9. Methodaccording to one of the claims 6 to 8, wherein the method involve thestep of joining opposed ends of the first and second fabric portions ofthe fabric to make a longer fabric by placing in contact a respectivefree yarn of one portion with a respective corresponding free yarn ofthe other portion and interconnecting and encapsulating said contactingyarns in said matrix material to form a homogeneous length of fabric.10. Method according to one of the claims 6 to 9, wherein the step ofinterconnecting said contacting free yarns includes the step of joiningsaid free yarns before encapsulation in said matrix material.
 11. Methodaccording to one of the claims 6 to 10, wherein the method include thestep of joining the opposed loop bearing ends of two first sections offabric by interdigitating the loops of the opposed ends and theninterconnecting the two portions with a pintle.
 12. Method according toone of the claims 6 to 11, wherein the method includes the step ofproviding a plurality of apertures in the matrix material in lateraloffset disposition relative to the yarns and extending throughout thematerial.
 13. Method according to one of the claims 6 to 12, wherein theapertures are formed during the encapsulation of the yarns by placingeach of the array of yarns and/or turned back yarns and/or joined yarnsinto a respective groove of a mould comprising upstanding pins servingto form said apertures in said material and then encapsulating theyarns, within the matrix material of the mould.